The present invention relates to a method of detecting the position of stacks of blanks for supply to a cigarette packing machine.
In the packing of cigarettes, stacks of blanks, each comprising a number of superimposed blanks, are fed individually to the input of a packing machine.
Normally, the stacks of blanks are originally arranged on a pallet in a number of superimposed layers separated by rigid boards, and in a number of side by side rows in each layer; the pallet so loaded is located in a given standard position close to the input; and the packing machine is normally equipped with an automatic transfer unit by which each stack is located, is removed from the relative row in the relative layer, and is fed to the input.
Known automatic transfer units normally comprise a pickup head for removing each stack off the pallet, and which is associated with an at least four-axis operating machine for imparting to the pickup head the movements required to pick up the stack. Known automatic transfer units also comprise a sensor device, normally movable with the pickup head, for determining the position and orientation of the stack, and for enabling a central control unit to accurately control the pickup movements. In this connection, it should be pointed out that the location of each stack is a xe2x80x9cfinal locationxe2x80x9d, seeing as how the central control unit already knows from the outset the shape and size of the blanks, a presumed (standard) position of the pallet with respect to the operating machine, a presumed distribution of the layers of stacks on the pallet, a presumed position and orientation of each row of stacks in the relative layer and of each stack in the relative row, and therefore a presumed position and orientation of each stack on the relative board.
Before each stack is removed (from the free top layer on the pallet), the sensor device takes a first reading to determine the height of the board supporting the layer containing the stack to be removed (this is normally done once for each layer, or may even be dispensed with if the operating machine is designed to move the pallet vertically so that the board supporting the stack to be removed is always set to a given fixed height), and then takes a second reading to determine the position and orientation of the stack on the board.
Using known sensor devices, the second reading is made by moving the sensor device in an observation plane, parallel to the plane of the board supporting the stack and over the top of the stack, and about the presumed position of the projection of the stack in the observation plane, and by determining the position of at least two (but normally three) conspicuous points of the top blank in the stack.
Taking the second reading as described above involves several drawbacks on account of the position and orientation of the stack being determined on the basis of the position and orientation of the top blank, i.e. without taking into consideration the possibility, as often occurs, of the stack being deformed, so that the horizontal position of the top blank no longer corresponds, when the stack is removed, to the position of the bottom blank, which is the one normally engaged by the pickup head to supply the stack to the packing machine.
In other words, the method employed by known sensors of the type described above may result in mislocation of the stack, and also in possible damage to the stack by the pickup head.
It is an object of the present invention to provide a method of detecting the position of stacks of blanks for supply to a cigarette packing machine, designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a method of detecting the position of stacks of blanks for supply to a cigarette packing machine; said stacks having respective bases resting on a plane; and the method comprising the step of moving a sensor along a line parallel to said plane and extending alongside said stacks in a given direction to determine the position and orientation of each said base with respect to said line by determining a contour of a lateral edge of at least one given blank, in each said stack, located close to the relative said base.